The activity response of the antioxidant enzymes glutathione peroxidase (GPx), glutathione reductase (GR) and the contents of thiobarbituric reactive substances (TBARS) were investigated in rats exposed to lead. The enzyme activities were determined in the liver, kidney and heart of male and female rats which were received 100 mg and 1000 mg of lead acetate per liter water for 18 weeks. The statistical analyses indicated the differences related to the organs and to the sex of animals. Administration of lead evoked decrease of GPx activity in the kidney of both male and female rats. On the contrary, GPx activity increased in the heart of female rats, while in the male rats the higher dose of lead evoked a decrease in activity. In the kidneys of male rats and in the heart of female rats thiobarbituric acid reactive substances (TBARS), an indicators of oxidative stress, significantly increased in rats which were given the high lead dose. Most likely the observed changes could be a compensatory response to different lead accumulation in the male and female organs and also the possible distinct mechanisms in ROS elimination.